1. Field of Invention
The invention is related to an actuator, comprising a housing which contains a screw mechanism and a motor, said screw mechanism comprising a nut and a screw, one of which is rotatably supported with respect to the housing, such that upon relative rotation of the nut and the screw a linear movement of one of said nut and screw is obtained.
2. Description of Related Art
In certain applications, such as actuators for disc brakes, clutches etcetera, it is desirable to limit the overall dimensions and possibly the weight as much as possible. According to the invention, a compact layout may be obtained in that at least a rotatable component of the drive, e.g. the rotor of the motor, is rotatably supported on the screw which is rotatably supported with respect to the housing.
In particular, in case the screw is rotatably supported with respect to the housing by means of a support bearing, the screw may be integrated with the outer ring of the support bearing, such that the rotor of the motor, by means of an auxiliary bearing, is rotatably supported on the outer ring of the support bearing.
The support bearing is preferably accommodated with the auxiliary bearing. In such embodiment, a compact and stiff support for the rotor and screw is obtained.
The linear movement provided by the actuator usually generates a force, e.g. in the case of a disc brake for clamping the brake pads onto the brake disc.
As a result of the inevitable flexibility of the actuator and the system to which said actuator is connected, elastic deformations are also generated.
In so far as these deformations are axial-symmetric with respect to the screw mechanism, no problems occur as to the proper function of the actuator. However, in certain cases, and in particular in the case of disc brakes, loads are generated which are eccentric with respect to the actuator.
The eccentricity is to be attributed to the asymmetric shape of the brake calliper, in particular of the claw piece thereof which carries the brake pads and which accommodates the brake disc sideways.
Upon pressing the brake pads onto the brake disc, the claw piece is loaded in bending, which bending action is also transferred onto the housing of the actuator. As the screw mechanism is supported within the housing, said mechanism may become exposed to bending as well.
The screw mechanism is however rather vulnerable with respect to misaligned forces, in such a way that the proper function may be hampered and that damage may occur.